The initial phase of this research project was designed to identify factors useful for prediction of pulmonary embolism. Hospitalized patients were classified as to their risk of pulmonary embolism through clinical and Doppler ultrasound examination. Patients in the upper third of the risk range were randomized into one group which received frequent surveillance (three times a week) and a comparison group was not subjected to such repeated examinations except upon sepcific request by the patient's physician. A total of 7271 admissionf of 6530 patients have been studied. The data have been entered onto computer tapes. Analysis will be directed toward 1) verifying and possibly extending previously identified risk factors, and 2) assessing the impact of frequent surveillance upon the occurrence of pulmonary embolism. Bibliographic references: Sigel, B., Felix, Jr., W.R., Justin, J.R., Popky, G.L., Mark, R., Williams, J., Gibson, R.J., Parker, J.A., Ipsen, J. and Mausner, J. Prospective Identification of the Pulmonary Embolism Prone Patient Employing Multi-Variable Risk Factor Analysis. in: Thromboembolism: Aetiology, Advances in Prevention and Management, pp. 181-191. Medical & Technical Publishing Co., Ltd., Lancaster, England, 1975.